<template>
  <ul class="list">
    <li
      class="item"
      v-for="key of letters"
      :key="key"
      :ref="key"
      @touchstart.prevent="handleTouchStart"
      @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      @click="handleLetterClick"
    >{{key}}</li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null,
      letterIndex: 0
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (!this.touchStatus) return false
      if (this.timer) {
        clearTimeout(this.timer)
      }

      this.timer = setTimeout(() => {
        const touchY = e.touches[0].clientY - 79
        const index = Math.floor((touchY - this.startY) / 20)
        if (this.letterIndex === index) return

        if (index >= 0 && index < this.letters.length) {
          this.$emit('change', this.letters[index])
          this.letterIndex = index
        }
      }, 8)
    },
    handleTouchEnd () {
      this.touchStatus = false
    },
    handleLetterClick (e) {
      this.$emit('change', e.target.innerText)
    }
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl';

.list {
  position: absolute;
  width: 0.4rem;
  top: 1.58rem;
  right: 0;
  bottom: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;

  .item {
    text-align: center;
    line-height: 0.4rem;
    color: $bgColor;
  }
}
</style>
